1. FIELD OF THE INVENTION
The present invention relates to an information output device such as laser beam printer or display for outputting data such as characters, and more particularly to an information output device having a merge circuit used to dot-expand data such as characters read from a font memory in accordance with positions on a screen, etc.
2. DESCRIPTION OF THE RELATED ART
In the laser beam printer or display, data such as characters is read from the font memory which stores the data and this character data is dot-expanded to a full-dot memory having a one-page capacity or one-screen capacity, and the dot data of the full-dot memory is read to print or display the data.
In order to position the data at any position in the full-dot memory, a merge circuit is required.
In the prior art, in order to arrange the data read from the font memory at any position in the full-dot memory, a shifter, a mask circuit, a merge buffer and a synthesization buffer have been used in the merge circuit. Because a large quantity of hardware is required as well as a large control microprogram, a long time is required to process this data. This significantly affects the overall throughput of a video data terminal including printer and display.
For example, in a display device disclosed in JP-B-58-36781, a display control unit comprises a font memory, an address decoder for specifying an address to read font data from the font memory, a counter, an adder, a row selector, a column shifter and a shift register. As the address decoder specifies an address, required characters or graphic pattern data are selected from the memory and read. The row selector selects an output row to display the pattern read from the memory. The column shifter shifts one row of data of the pattern supplied from the row selector to the left or right by the specified amount and supplies it to the shift register. The shift register stores one row of pattern data, throws away as many bits as the amount of horizontal shift at the right end and adds as many "0" bits as the amount of horizontal shift to the left end.